Xylene isomers are produced in large volumes from petroleum as feedstocks for a variety of important industrial chemicals. The most important of the xylene isomers is para-xylene, the principal feedstock for polyester, which continues to enjoy a high growth rate from large base demand. Ortho-xylene is used to produce phthalic anhydride, which supplies high-volume but relatively mature markets. Meta-xylene is used in lesser but growing volumes for such products as plasticizers, azo dyes and wood preservers. Ethylbenzene generally is present in xylene mixtures and is occasionally recovered for styrene production, but is usually considered a less-desirable component of C8 aromatics.
Among the aromatic hydrocarbons, the overall importance of xylenes rivals that of benzene as a feedstock for industrial chemicals. Xylenes and benzene are produced from petroleum by reforming naphtha but not in sufficient volume to meet demand, thus conversion of other hydrocarbons is necessary to increase the yield of xylenes and benzene. Often toluene is de-alkylated to produce benzene or selectively disproportionated to yield benzene and C8 aromatics from which the individual xylene isomers are recovered.
Methylation of toluene or benzene with oxygenates such as methanol has been proposed as a pathway to make xylene and to increase methyl to phenyl ratio in the aromatic complex to maximize xylene production. For the toluene methylation process there is a yield advantage to add methanol at various locations above the main feed injection point. The reactor is a transport riser style with the feed and catalyst flowing co-currently up the riser. In this riser style and operating conditions, there will be a catalyst velocity gradient in the radial direction in which some catalyst will slow down and begin to fall down along the riser wall. In addition, the high upward momentum of catalyst away from the wall does not allow the methanol injection from the side of riser to penetrate and mix into the main flow of catalyst. This decreases the methanol injection's effectiveness, and thus yield improvements may not be realized.
Accordingly, it is desirable to provide improved apparatuses for methylation of aromatic compounds such as toluene and benzene in an aromatics complex. Furthermore, other desirable features and characteristics of the present subject matter will become apparent from the subsequent detailed description of the subject matter and the appended claims, taken in conjunction with the accompanying drawing and this background of the subject matter.